Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
436 FOUS30 KWBC 171945 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Fri Oct 17 2025 Day 1 Valid 16Z Fri Oct 17 2025 - 12Z Sat Oct 18 2025 ...16Z Update... The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 2 Valid 12Z Sat Oct 18 2025 - 12Z Sun Oct 19 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN MISSOURI... ...2030Z Update... The most significant change this update was to shrink the Slight to just the Ozarks of southern Missouri. In coordination with LSX/St. Louis, MO forecast office, the Slight was removed from the St. Louis metro area. Much of the latest guidance suggests the heaviest rainfall will be concentrated in the Ozarks, where there is likely an upslope component allowing the rain to concentrate across the Ozarks. From St. Louis on north and east into Michigan, instability will be lesser, and the front organizing all of the rainfall will be more progressive, which will limit the flash flooding potential. Perhaps a greater factor than even the potential for heavy rainfall will be the antecedent extremely dry/drought conditions in place across all of the Midwest. While in the Ozarks, the terrain helps focus the rainfall, which in combination with leaf debris should increase the instances of flash flooding, given the peak in forecast rainfall in the Ozarks, once into Illinois, Indiana, and Michigan, even more extreme drought and the lack of topography should allow any heavy rain to be readily absorbed by the parched earth. Thus, the area remains in a Marginal, with a focus on any urban areas (Indiana suburbs of Chicago for example) or any flood- prone, low-lying areas. Wegman ...Previous Discussion... The latest models remain in good agreement on the overall sharpening of the mid to upper level trof across the mid section of the nation Saturday into early Sunday. Well defined upper difluence likely between the northern stream vort moving east southeast across the Central Plains and the southern stream vort moving east northeast across the Southern Plains. PW values will increase to 1 to 2+ standard deviations above the mean in this broad upper diffluent axis from eastern portions of the Southern Plains, northeastward into the Mid MS Valley and Great Lakes, along and ahead of the associated eastward moving frontal boundary. Model consensus is for a broad area of moderate to heavy rainfall amounts in this axis. All of this region has been very dry with relative soil moisture low, low stream flows and subsequently FFG values very high, which will be a detriment to widespread runoff issues. The previous slight risk area was shrunk considerably, focusing it where the HREF and RRFS means show higher probabilities for 1 and 2"+ amounts in the 12 hour period from 12Z Sat Oct 18 to 00Z Sun Oct 19 from northwest AR, across southern MO into southern IL. This region also corresponds to where the relative soil moisture is not as low as points farther to the northeast and southwest, although overall, still low. There may be a period of training of cells in the slight risk area during the first half of the day 2 period, before the convection begins to accelerate to the east and southeast during the second half of day 2. The previous marginal risk area was also decreased significantly, narrowing the eastern extent through the OH and TN Valleys. Oravec Day 3 Valid 12Z Sun Oct 19 2025 - 12Z Mon Oct 20 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE EASTERN GREAT LAKES INTO THE CENTRAL APPALACHIANS... ...2030Z Update... The inherited Marginal risk was expanded through the mountains of Pennsylvania and western/central New York with this update. While overall the line will be quite progressive, with any embedded convection moving along at a rapid pace along the front to the northeast, the combination of expected wind blowing more leaves down which will both be slippery and clog storm drains, and the terrain helping focus any rainfall into narrow valleys should result in isolated instances of flash flooding. Otherwise, little has changed in the forecast or expected rainfall, so no other significant changes were made. Wegman ...Previous Discussion... The amplifying mid to upper level trof across the mid section of the nation day 2, will continue to accelerate eastward day 3, becoming increasingly negatively tilted as it moves through the OH Valley, Central Appalachians, Mid- Atlantic and eastern Lakes. The fast eastward movement will continue to be a limiting factor for very heavy rainfall amounts and any widespread runoff issues. While FFG values are much lower across the eastern Lakes into the Upper OH Valley and Central Appalachians than areas farther south and west during the day 2 period, the aforementioned progressive nature of the day 3 system should preclude most areas exceeding FFG values. No changes made to the previous marginal risk area from the eastern Lakes, south into the Upper OH Valley and Central Appalachians. Oravec Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt